This invention relates generally to ink jet arrays including a plurality of ink jet channels wherein each channel includes a chamber, an inlet to the chamber, an orifice from the chamber, and transducer means coupled to the chamber for ejecting droplets of ink from the chamber as a function of the state of energization of the transducer means. More specifically, this invention relates to a simplified method of constructing an impulse ink jet apparatus.
In liquid droplet ejecting systems of the drop-on demand type, such as impulse ink jet printers, a piezoceramic transducer is used to cause expulsion of ink as droplets from a small nozzle or jet. An array of such jets is often utilized in high-speed, high-resolution printers where, as is well-known, the printing rate and printed image resolution is dependent upon the number of jets and spacing therebetween. In general, the closer the jets are to one another, the faster the images can be produced and the higher the resulting image resolution.
One suitable such printer is described in U.S. Pat. No. 4,459,601, issued July 10, 1984 to Stuart D. Howkins, assigned to the assignee of the present invention and incorporated herein by reference. In that arrangement, an ink jet apparatus of the demand or impulse type comprises a chamber and an orifice from which droplets of ink are ejected in response to the state of energization of a transducer which communicates with the chamber through a foot forming a movable wall. The transducer expands and contracts, in a direction having at least one component extending parallel with the direction of droplet ejection through the orifice, and is elongated in such direction, the electric field resulting from the energizing voltage being applied transverse to the axis of elongation.
One problem common to all high-speed, high-resolution, drop-on-demand ink jet printers occurs because the jets of an array are spaced very close to one another. That is, the response of one jet in an array to its drive voltage can be affected by the simultaneous application of a drive voltage to another nearby jet. This can result in a phenomenon, known in the art as "mechanical cross-talk", where pressure waves are transmitted through the solid material in which the jets are formed, or in another phenomenon, known in the art as "electrical cross-talk", where relatively large drive voltages necessary for substantial displacement of transducers utilized in the prior art cause the subsequent pulsing of an inappropriate jet.
While the risk of electrical cross-talk between ink jets in an array utilizing the teachings of U.S. Pat. No. 4,459,601 as discussed above will be minimized, the risk of mechanical cross-talk remains. One approach which alleviates this problem, however, is discussed in U.S. Pat. No. 4,439,780, issued Mar. 27, 1984 to Thomas W. DeYoung and Viacheslav B. Maltsev, assigned to the assignee of the present invention and incorporated herein and by reference. In that arrangement, an ink jet array comprises a plurality of elongated transducers coupled to a plurality of ink jet chambers, the transducers being supported only at their longitudinal extremities. The support at the extremity remote from the chamber is provided such that no longitudinal motion along the axis of elongation of the transducers occurs, while the other extremity includes bearing means which substantially preclude lateral movement of the transducers transverse to their axis of elongation but permit the longitudinal movement thereof along the axis, thus minimizing mechanical cross-talk between ink jets within the array. Other characteristic problems which are encountered in the implementation of high-speed, high-resolution impulse ink jet printers do not impact so much upon their operation, but indeed impact upon their fabrication. For example, the relatively small size of component parts used in densely packed arrays make them difficult to handle. An easily fabricated ink jet array is, therefore, preferred.
One early approach to the above-described problem is disclosed in U.S. Pat. No. 4,072,959, which issued to Rune Elmqvist. As discussed therein, a recorder operating with drops of liquid includes a comb-shaped piezoelectric transducer arranged such that individual teeth of the comb are associated respectively to a densely-packed array of ink jet chambers. The teeth, actually a series of elongated transducers, are energized by electrodes which apply a field transverse to the axis of elongation. Each of the transducers is immersed in a common reservoir such that energization of one transducer associated with one chamber may produce cross-talk with respect to an adjacent chamber or chambers. In other words, there is no fluidic isolation from chamber to chamber between the various transducers or more accurately, segments of the common transducer. In addition to such cross-talk, the construction shown in the Elmqvist patent poses a requirement for a non-conductive ink.
Layered or laminated ink jet structures have also been utilized to facilitate fabrication of ink jets. For example, U.S. Pat. No. 4,392,145, issued July 5, 1983 to Walter R. Parkola, assigned to the assignee of the present invention and incorporated herein by reference, shows a multi-layer ink jet apparatus which includes a plurality of channels comprising chambers including inlets and orifices and transducers coupled to the chambers. The various channels are located in different layers that stagger with respect to a plane transverse to the layers so as to achieve a high density array of ink jet orifices. In such a manner, the apparatus provides a high degree of precision which is required in densely packed multi-channel impulse ink arrays.
While the edge-wise ejecting orifice arrangement provided by Parkola facilitates the manufacture of such devices, there has been little effort within the prior art to ease the assembly of ink jet printers having droplet ejection orifices in a planar array. Typically in the past, manufacturing of ink jet printers required the use of a plurality of mechanical fasteners such as screws to compress the relatively thick plates forming the ink flow paths against the print head body in order to avoid mechanical cross-talk caused by leakage of ink between chambers in a multi-channel array. Such mechanical fasteners necessitate additional drilling and boring steps which only complicate the assembly process. It would, therefore, be desirable to provide an ink jet apparatus and method for fabricating same which fosters manufacturing expediencies and, at the same time, minimizes mechanical cross-talk and leakage during operation.